Skin, hair, and nails are subject to insults by many extrinsic and intrinsic factors. Extrinsic factors include ultraviolet radiation (e.g., from sun exposure), environmental pollution, wind, heat, humidity extremes, harsh surfactants, abrasives, and the like. Intrinsic factors include chronological aging and other biochemical changes from within the skin, hair, or nails. Whether extrinsic or intrinsic, these factors result in visible signs of skin, hair, and nail aging and environmental damage (e.g., such as sunlight damage, smoke damage, and damage from pollutants such as nitrogen oxides, sulfur oxides, ozone, and metals such as lead).
In addition to the visible signs that result from damage and/or aging of keratinous tissue (e.g., hair, skin, and nails), changes also occur in the keratinous tissues' chemical and/or physical properties. For instance, healthy undamaged human hair is hydrophobic. However, when the hair becomes oxidized and/or damaged, the hair becomes hydrophilic. Furthermore, some regions of hair may be more damaged than others, leading to hydrophilic hair in some areas but hydrophobic in others. This heterogeneity of properties makes it difficult to deliver a consistent, uniform benefit to the entire head of hair (e.g., conditioning, coloring, etc.), since the varying hair properties affect the performance of the hair care composition that is applied.
Similar problems exist with the application of skin care products to skin. Skin undergoes a change in surface energy when it is damaged and/or aged. As with hair, the properties of the skin thus vary across different regions of the skin's surface. This heterogeneity makes it difficult to deliver a consistent, uniform benefit to the entire skin surface to be treated, since the varying skin properties affect the performance of the skin care composition that is applied.
In addition, certain materials in personal care formulations can undesirably accumulate on keratinous substrates (e.g. hair and/or skin) to create aesthetic or functional negatives. This can result from incompatibility of the materials with compositions made to cleanse and/or remove them. For example, silicone polymer-based conditioner products can excessively accumulate on the hair surface with repeated application, resulting in a greasy look and/or feel. Ideally, the conditioning agent would be removed with each shampooing and a new layer deposited.
Furthermore, many desired benefit agents are not compatible (e.g., soluble, miscible, dispersible) with the preferred delivery vehicle. For example, it can be difficult to formulate, stabilize, and/or deliver a hydrophobic benefit agent in a predominantly water-based (hydrophilic) composition.
Accordingly, there is a need for personal care compositions that provide a uniform benefit to keratinous tissue regardless of the keratinous tissue's non-uniformity of chemical and/or physical properties. Furthermore, there is a need for personal care compositions that do not undesirably accumulate on keratinous tissue despite removal efforts. In addition, there is a need for personal care compositions that can deliver benefit agents that are considered incompatible with the preferred delivery vehicle.